We are studying one of 40 genes defined mutationally to affect muscle in the nematode Caenorhabditis elegans. The proteins encoded by some of these genes is now known, and with time, the products of all 40 genes will be learned by using powerful methods available in C. elegans such as transposon tagging and the emerging complete physical map of the genome combined with transgenic mutant rescue. As more of the gene products are identified and their functions elucidated, we will gain a better understanding about how muscle is assembled and contraction is regulated. unc-22 is one of these genes originally identified mutationally, cloned by transposon tagging, and shown to encode an approx. 600,000 dalton polypeptide, located in the myosin-containing A-bands. Its unusual "twitching" phenotype, genetic evidence for interaction with myosin, and its location in A-bands, suggested that it had an important role in regulating the activity of myosin. Recently, I finished sequencing the 48.2 kb region containing the unc-22 gene and supplementary cDNA sequence. Conceptual translation yields an unusually large polypeptide of 6048 amino acids (668,520 daltons) which consists almost entirely of a single protein kinase domain and multiple copies of 2, 100 residue motifs. One of these motifs is a member of the immunoglobulin superfamily. I found all 3 domains in the myosin light chain kinase of chicken smooth muscle. By comparison to the unc-22 data, J. Trinick has found both motifs I and II in similar arrangement in titin, a very large polypeptide (3 x 10 6 daltons) of vertebrate striated muscle and closely associated with thick filaments but having an unknown function. Our hypothesis is that the motifs in unc-22 protein bind to the thick filament to coordinate the activity of many myosins and that the vertebrate analogs may have similar roles. Our goals include: (1) by studying expressed portions of unc-22 protein in vitro, to determine which combinations of motifs bind to which thick filament components, (2) as which portions of the protein are crucial for function, by determining what is the minimum portion of unc-22 that can function in transgenic experiments, and how much sequence can be deleted by mutation with little effect on function, (3) through sequence analysis of known unc-22 mutants, find out which residues or regions are critical for assembly and responsible for "twitching" and (4) we will determine whether there are other unc-22-like genes in C. elegans, and if so, what their functions might be.